Fluid-working machine and operating method

Abstract

A fluid-working machine has a plurality of working chambers, e.g., cylinders, of cyclically changing volume, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber to each manifold, and electronic sequencing means for operating said valves in timed relationship with the changing volume of each chamber, wherein the electronic sequencing means is arranged to operate the valves of each chamber in one of an idling mode, a partial mode in which only part of the usable volume of the chamber is used, and a full mode in which all of the usable volume of the chamber is used, and the electronic sequencing means is arranged to select the mode of each chamber on successive cycles so as to infinitely vary the time averaged effective flow rate of fluid through the machine.

What is claimed is: 
     
       1. A method of operating a fluid-working machine having a plurality of working chambers of cyclically changing volume, said working chambers comprising cylinders within which pistons are arranged to reciprocate, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber of said working chambers to each manifold, the method comprising:
 operating the valves of at least one of said working chambers in a partial motoring mode in which only part of the usable volume of the at least one working chamber is used; and 
 determining a mode of each working chamber of said working chambers on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the machine according to a demand level; and operating the valves of each of said working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, and (ii) said partial motoring modes, wherein the sequence of modes of operation is based upon a function of the error between the measured and demanded pressure. 
 
     
     
       2. A method of operating a fluid-working machine having a plurality of working chambers of cyclically changing volume, said working chambers comprising cylinders within which pistons are arranged to reciprocate, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber of said working chambers to each manifold, the method comprising:
 operating the valves of at least one of said working chambers in a partial motoring mode in which only part of the usable volume of the at least one working chamber is used; and 
 determining a mode of each working chamber of said working chambers on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the machine according to a demand level; and operating the valves of each of said working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, and (ii) said partial motoring modes, wherein the sequence of modes of operation is based upon the time history of past systems responses to past decisions. 
 
     
     
       3. A fluid-working machine comprising:
 a plurality of working chambers of cyclically varying volume, said working chambers comprising cylinders within which pistons are arranged to reciprocate; 
 a high-pressure fluid manifold; 
 a low-pressure fluid manifold; 
 at least one valve linking each working chamber of said working chambers to each manifold; and 
 a controller having a configuration to operate the valves of at least one of the said working chambers in a partial motoring mode in which only part of the usable volume of the at least one working chamber is used, 
 wherein the controller is further configured to: vary the time averaged effective flow rate of fluid through the machine according to a demand level, and operate the valves of each of the working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, (ii) said partial motoring modes, wherein the sequence of modes of operation is based upon a function of the error between the measured and demanded pressure. 
 
     
     
       4. A fluid-working machine comprising:
 a plurality of working chambers of cyclically varying volume, said working chambers comprising cylinders within which pistons are arranged to reciprocate; 
 a high-pressure fluid manifold; 
 a low-pressure fluid manifold; 
 at least one valve linking each working chamber of said working chambers to each manifold; and 
 a controller having a configuration to operate the valves of at least one of the said working chambers in a partial motoring mode in which only part of the usable volume of the at least one working chamber is used, 
 wherein the controller is further configured to: vary the time averaged effective flow rate of fluid through the machine according to a demand level, and operate the valves of each of the working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, (ii) said partial motoring modes, wherein the sequence of modes of operation is based upon the time history of past systems responses to past decisions. 
 
     
     
       5. A machine comprising: a plurality of working chambers of cyclically changing volume; a high-pressure fluid manifold; a low-pressure fluid manifold; at least one valve linking each working chamber to each manifold; and a controller having a configuration to: determine a mode of each working chamber on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the machine according to a demand level, and operate the valves of each of the working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, (ii) partial stroke modes in which only part of the usable volume of the working chamber is used and (iii) full stroke modes in which all of the usable volume of the working chamber is used. 
     
     
       6. The machine of  claim 5 , wherein the demand level is varied in use. 
     
     
       7. The machine of  claim 5 , wherein the partial stroke modes comprise use of only a small fraction of the usable volume of the working chambers, and wherein the small fraction is one in which valve actuations are delayed to almost the end of the stroke such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation. 
     
     
       8. The machine of  claim 5 , wherein the partial stroke modes comprise use of only a small fraction of the usable volume of the working chambers, and wherein the small fraction is one that provides sufficient stability of valve operation at the low flow end. 
     
     
       9. The machine of  claim 5 , wherein, in the partial modes, valve actuations are delayed to almost an end of a stroke such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation. 
     
     
       10. The machine of  claim 5 , wherein the partial stroke modes are part stroke motoring modes in which the transition from intake from the high-pressure manifold to intake from the low pressure manifold happens a small fraction after top dead center, wherein the small fraction is one in which valve actuations are such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation. 
     
     
       11. The machine of  claim 5 , wherein the sequence of modes of operation is tailored for one or more of the smoothest flow result, the most seamless change in audible noise, minimal pressure ripple, and optimum actuator motion. 
     
     
       12. A machine comprising: a plurality of working chambers of cyclically changing volume; a high-pressure fluid manifold; a low-pressure fluid manifold; at least one valve linking each working chamber to each manifold; and a controller having a configuration to: vary the time averaged effective flow rate of fluid through the machine according to a demand level, and operate the valves of each of the working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, (ii) partial stroke modes in which only part of the usable volume of the working chamber is used and (iii) full stroke modes in which all of the usable volume of the working chamber is used. 
     
     
       13. A method of operating a fluid-working machine having a plurality of working chambers of cyclically changing volume, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber to each manifold, the method comprising:
 determining a mode of each of the working chambers on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the fluid-working machine according to a demand level; and 
 operating the valves of each of the working chambers to select the determined mode in one of (i) an idling mode, (ii) a partial stroke mode in which only part of the usable volume of the working chamber is used, and (iii) a full stroke mode in which all of the usable volume of the working chamber is used, 
 wherein the sequence of modes of operation is tailored for one or more of the smoothest flow result, the most seamless change in audible noise, minimal pressure ripple, and optimum actuator motion. 
 
     
     
       14. A method of operating a fluid-working machine having a plurality of working chambers of cyclically changing volume, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber of said working chambers to each manifold, the method comprising:
 determining a mode of each working chamber of said working chambers on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the machine according to a demand level; and 
 operating the valves of each of said working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) partial stroke modes in which only part of the usable volume of the chamber is used and (ii) full stroke modes in which all of the usable volume of the working chamber is used. 
 
     
     
       15. The method of  claim 14 , wherein
 the valves of each of said working chambers are operated to select the determined mode in accordance with the operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) the partial stroke modes in which only part of the usable volume of the chamber is used, (ii) the full stroke modes in which all of the usable volume of the working chamber is used, and (iii) idling modes. 
 
     
     
       16. The method of  claim 14 , wherein the demand level is varied in use. 
     
     
       17. The method of  claim 14 , wherein the partial stroke modes comprise use of only a small fraction of the usable volume of the working chambers, and wherein the small fraction is one in which valve actuations are delayed to almost the end of the stroke such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation. 
     
     
       18. The method of  claim 14 , wherein the partial stroke modes comprise use of only a small fraction of the usable volume of the working chambers, and wherein the small fraction is one that provides sufficient stability of valve operation at the low flow end. 
     
     
       19. The method of  claim 14 , wherein, in the partial stroke modes, valve actuations are delayed to almost an end of a stroke such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation. 
     
     
       20. The method of  claim 14 , wherein the partial stroke mode is a part stroke motoring mode in which the transition from intake from the high-pressure manifold to intake from the low pressure manifold happens a small fraction after top dead center, wherein the small fraction is one in which valve actuations are such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation. 
     
     
       21. The method of  claim 14 , wherein the sequence of modes of operation is tailored for one or more of the smoothest flow result, the most seamless change in audible noise, minimal pressure ripple, and optimum actuator motion.